Electric circuit for energizing and deenergizing an exciter lamp of a talkie projector

ABSTRACT

The electric circuit for energizing and deenergizing an exciter lamp of a talkie projector having an optical sound reproducing head in accordance with the present invention comprises a constant current circuit selectively energized by an electric source. The constant current circuit includes a current control output transistor and an error current detecting amplifier. The exciter lamp is connected to the output of the constant current circuit as a load thereof so that the exciter lamp is permitted to be energized or deenergized by the constant current circuit upon energization or deenergization thereof.

United States Patent 11 1 Matsui et a]. Sept. 2, 1975 1 ELECTRIC CIRCUITFOR ENERGIZING $247,451 4/1966 Hauck 315/311 x AND DEENERGIZING AN C TEL M \Yollnhals 322/2 3,):

, e e OF A TALKIE PROJECTOR 3,588,672 6/1971 Wilson 323/4 [75]Inventors: Koji Matsui, Shiki; Kiyoyuki Arai,

Tokyoboth of Japan Primary E.\'aminer.lames W. Lawrence 73 Assignee; c lCompany Li i d, T k Assistant Examiner-E. R. LaRoche Japan Almrney,Agent, or Firm-Oblon, Fisher, Spivak, McClelland & Maier [22] Filed:Apr. 25, 1974 [2]] Appl. No.: 464,218 [57] ABSTRACT The electric circuitfor energizing and deenergizing an [30] Foreign Apphcatlon Priority Dataexciter lamp of a talkie projector having an optical May 2, 1973 Japan48-48474 sound reproducing h d in accordance with the present inventioncomprises a constant current circuit se- [52] 315/307; 315/135; 315/205;lectively energized by an electric source. The constant 0 315/208;315/29]; 315/3] 1; 323/4 current circuit includes a current controloutput tran- [5 l l G05F 1/56; H05B 39/04 sistor and an error currentdetecting amplifier. The ex- [58] Field of Search 315/94. 101, 107, 135,Citer lamp is connected to the output of the constant 315/136 200current circuit as a load thereof so that the exciter 31 323/4 lamp ispermitted to be energized or deenergized by the constant current circuitupon energization or de- [56] References C'ted energization thereof.

UNITED STATES PATENTS 3,246,233 4/1966 Hcrz 323/4 5 4 Drawmg F'guresPATEI'H ED SEP 21975 Fig ELECTRIC CIRCUIT FOR ENERGIZING ANDDEENERGIZING AN EXCITER LAMP OF A TALKIE PROJECTOR BACKGROUND OF THEINVENTION The present invention relates to an electric circuit forenergizing and deenergizing an exciter lamp of a talkie projector havingan optical sound reproducing head.

In general. the life of a projector lamp for projecting the image bornon a film and an exciter lamp for the optical sound reproducing headused in a talkie projector is several tens hours at the longest. Inorder to prolong the life of a projector lamp, preliminary lightingprocess has been applied. However, no such process has been applied toprolong the life of an exciter lamp thereby suffering from the shortlife of the exciter lamp. Although the price of an exciter lamp isrelatively low in comparison with a projector lamp, it has often beendifficult to obtain the exciter lamp in the market. Further, since theexciter lamp is generally used in a D.C. turn-on system, an excessinitial rush current is flow through the exciter lamp if the lamp isinserted into the circuit of the electric source under the condition thecircuit is held in the closed state. thereby tending the exciter lamp tobe broken. Further. in order to reduce the bum components caused by theexciter lamp when a conventional electric source having resistors,capacitors and ripple filters is used, electrolytic capacitors of fairlylarge size and capacity are required thereby causing problems of thespace and the cost therefor. A system has also been developed in whichthe exciter lamp is turned on by high frequency electric current, butsuch a system also suffers from the problems described above.

The present invention aims at avoiding the above described shortages ofthe prior art electric circuit of the exciter lamp of the talkieprojector. I

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a novel and useful electric circuit for energizing anddeenergizing an exciter lamp of a talkie projector having an opticalsound reproducing head which avoids the above described shortages of theprior art electric circuit of an exciter lamp of a talkie projector.

Another object is to provide a novel and useful electric circuit of thetype described above which is simple in construction and whichpositively prevents the initial rush current from flowing through theexciter lamp when inserted into circuit of the electric source in theclosed state thereby insuring long life of the exciter lamp while theripple is extremely reduced so as to' avoid the hum components in thesound reproduction.

The above objects are achieved in accordance with the characteristicfeature of the present invention by the provision of an electric circuitfor energizing and deenergizing an exciter lamp of a talkie projectorhaving an optical sound reproducing head, comprising a constant currentcircuit selectively energized by an electric source and including acurrent control output transistor and error current detecting amplifierhaving an error current detecting transistor and a constant currentdetecting resistor. said'exciter lamp being connected to said constantcurrent circuit as a load thereof. thereby permitting said exciter lampto be energized or deenergized by said constant current circuit byconnecting or disconnecting said error current detecting amplifier to orfrom said electric source.

By such a construction, the exciter lamp is supplied with a constantcurrent without suffering from the initial excess rush current each timethe exciter lamp is energized by the constant current circuit therebyinsuring the long life of the exciter lamp while the ripple is reducedso as to avoid the hum components in the sound reproduction.

Since the current required for actuating the error current detectingamplifier is very low, the switch and other parts used can be madesimple, compact and of a low capacity, while the life of the switch isextremely prolonged.

Further, since the voltage at the constant current detecting terminal ofthe constant current circuit may be used as an electric source of aconstant voltage, a relay or solenoid may be energized thereby in placeof the constant current detecting resistor together with the exciterlamp.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagram showing the firstembodiment of the electric circuit constructed in accordance with thepresent invention;

FIG. 2 is a diagram similar to FIG. I but showing a modificationthereof;

FIG. 3 is a diagram showing a second embodiment of the electric circuitof the present invention; and

FIG. 4 is a diagram similar to FIG. 3 but showing a modificationthereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1showing the first embodiment of the present invention, the constantcurrent circuit comprises a current control output transistor O with itscollector connected to one terminal B of an electric source, a constantcurrent detecting resistor R connected at its one end to the emitter ofthe output transistor 0 an error current detecting transistor Q with itscollector connected to the terminal B through a collector resistor R;;,a constant voltage diode D connected between the emitter of thetransistor Q and the other end of the constant current detectingresistor R, and a switch S connected between the collector resistor Rand the collector of the transistor 0,, the base of the outputtransistor Q being connected to the collector of the transistor 0 whilethe base of the transistor Q. is

connected to a junction between the emitter of the output transistor 0and the one end of the constant current detecting resistor R. Thetransistor 0 serves as an error current detecting amplifier, and theterminal voltage of the constant current detecting resistor R iscompared with a reference voltage obtained by the sum of thebase-emitter voltage of the transistor Q, and the terminal voltage ofthe constant voltage diode D so that the current flowing through theresistor R is detected so as to render the same to be constant.

In accordance with the characteristic feature of the present invention,the exciter lamp L is connected at its one end to the other end of theconstant current detecting resistor R while the other end of the lamp Lis connected to the other terminal of the electric source. i.e.. to theearth. Thus. the exciter lamp L is connected to the constant currentcircuit as a load thereof.

In operation, when the switch S is opened, no current is supplied to thetransistor Q and, hence,the output transistor 0,, is held innon-conductive state so that the constant current circuit is held inopened state thereby extinguishing the exciter lampL; When the'switch S'is closed, a current is supplied to the base of the output lampL'through the constant current detecting resistor R to turn the exciterlamp L on, wherein the terminal loltage of the resistor R is comparedwith the sum of :he. base-emitter voltage of the error current detecting:ransistor Q and the terminal voltage of the constant.

loltage diode D so as to insure the constant current to )e supplied tothe exciter lamp L. 1 t

FIG. 2 shows a modification of FIG. 1,: wherein a lWitCh S is providedin place of the switch S of FIG. 1 vhich is connected at its one contactto the junction of he base of the output transistor Q and the collectorof he transistor O to which the resistor R,,.is also coniected, theother contact being connected to .the other erminal of the electricsource, i.e., to the earth.

The operation of the circuit of FIG. 2v is similar to hat of FIG. 1,except that the lamp L is energized when he switch 5' is opened so as tosupply-current to the ransistors O, and Q while, when the switch S is:losed, the lamp is deenergized. I

FIG. 3 shows the second embodiment of the present nvention. The circuitof FIG.'3 is substantially similar that of FIG. 1, except that the errorcurrent detectng amplifier is constructed by the transistor 0 and aurther transistor Q provided in place of the diode D f FIG. 1, thecollector of the transistor Q being con-,

ectedto the terminal B of the electric source through collector resistorR as well as to the base of the outut transistor Q while the base of thetransistor Q is onnected to the collector of the transistor Q and themitter of the transistor O is connected to the emitter f the transistor0,. In theembodimentof FIG. 3, the a se of the transistor Q is connectedto ajunction beveen a first voltage dividing resistor R and a secondoltage dividing resistor R connected in seriesto each ther, the oppositeend of the resistor R being conected to the junction between thecollector of the outut transistor Q and the one end of the resistorRwhile 1e opposite end of the resistor R is connected to thether end ofthe resistor R. Thus, thedivided voltage lthe terminal voltage of theresistor R obtained by the :sistors R,, R is compared with the referencevoltage btained by the base-emitter voltage of the transistor so as toinsure the constant current supplied by the :sistor R to the lamp L.

In operation, in like manner as in the case. ofFIG. 1,

hen the switch S is closed, the constantcurrent circuit energized toturn the lamp L on, while, when the vitch S is opened, the constantcurrent circuit is )ened to extinguish the lamp L." 7

FIG. 4 shows a modification of FIG. 3. The ent of FIG. 4 is similartoFIG. 3 except that the (itch S is provided in place of the switch S ofFIG. 3 like manner as in the caseof'FIG. 2 in which the /itch s' isprovided inplace a theswitch S Orr n, 1.

embodi- The operation or the embodiment of FIG. 4 is similar to that ofFIG. 3,.but, when the switch S is'opened, the constant current circuitis energized so that the lamp L is energized while, when the switch S isclosed, the

' lamp L is'extinguished.

We claimz 1.1 Electric circuit for energizing and deenergizing'anexciter lamp of a talkie projector having an optical sound reproducinghead, comprising a constant circuit connected between one terminal of anelectric source and one end of said exciter lamp the other end of whichis connected .to the other terminal of said electric source, saidconstant currentcircuit comprising a current control output transistorwith its emitter and collector connected between said-one terminal ofsaid electric sourceand said exciterlamp forenergizing said exciter,lamp when rendered to be conductive, a constantcurrent detectingresistor connected between said current control output transistor andsaid exciter lamp, an error current detecting transistor with acollector resistor thereof connected to said one terminal ofsaidelectric source and its base connected to a junction between.saidcurrent control output transistor and said constant currentdetecting resistor, the base of said current control output transistorbeing connected to a junction between said collector resistor of saiderror current detecting transistor and the collector of said errorcurrent detectingtransistor the emitter of which is connected to ajunction between said constant current detecting resistor and saidexciter lamp, and a switch connected to the collector circuit of saiderror current detecting transistor for opening and closing the collectorcurrent flowing therethrough thereby permitting said curr'ent c'ontroloutput transistor to be rendered conductive by the operation of saidswitch so as to turn on said exciter lamp.

2. Electric circuit according to claim 1, wherein a constant voltagediode is connected between the emitter of said error current detectingtransistor and said junction between said constant current detectingresistor and said exciter lamp, and said switch is connected betweensaidcollector resistor of said error current detecting transistor'andthe collector of said error current detecting transistor.

3. Electric current according to claim 1, wherein a constant voltagediode is connected between the emit ter of said error current detecting.transistor and said junction between said constant current detectingresistor and said exciter lamp,'and said switch is connected between thecollector of said error current detecting transistor and said otherterminal of said electric source.

4.Electric circuit according to claim 1, wherein the base of saidcurrent control output transistor-is con nected through thecollector-base path of a furthertransistor to the collector of saiderror current detecting transistor, said collector of said furthertransistor beingco nnected to said oneterminal of said electric sourcethrough a collector resistor thereof while the emitter thereof isconnected to the emitter of said error current detecting transistor, andthe base of said error resistor andsaid exciter larnp throughya secondvoltage t dividing resistor, said switch being connected between thecollector of said error current detecting transistor and said collectorresistor of said error current detecting transistor.

5. Electric circuit according to claim 1, wherein the base of saidcurrent control output transistor is connected through the collector andthe base of a further transistor to the collector of said error currentdetecting transistor, said collector of said further transistor beingconnected through a further collector resistor to said one terminal ofsaid electric source while the emitter thereof is connected to theemitter of said error curlector of said error current detectingtransistor.

1. Electric circuit for energizing and deenergizing an exciter lamp of atalkie projector having an optical sound reproducing head, comprising aconstant circuit connected between one terminal of an electric sourceand one end of said exciter lamp the other end of which is connected tothe other terminal of said electric source, said constant currentcircuit comprising a current control output transistor with its emitterand collector connected between said one terminal of said electricsource and said exciter lamp for energizing said exciter lamp whenrendered to be conductive, a constant current detecting resistorconnected between said current control output transistor and saidexciter lamp, an error current detecting transistor with a collectorresistor thereof connected to said one terminal of said electric sourceand its base connected to a junction between said current control outputtransistor and said constant current detecting resistor, the base ofsaid current control output transistor being connected to a junctionbetween said collector resistor of said error current detectingtransistor and the collector of said error current detecting transistorthe emitter of which is connected to a junction between said constantcurrent detecting resistor and said exciter lamp, and a switch connectedto the collector circuit of said error current detecting transistor foropening and closing the collector current flowing therethrough therebypermitting said current control output transistor to be renderedconductive by the operation of said switch so as to turn on said exciterlamp.
 2. Electric circuit according to claim 1, wherein a constantvoltage diode is connected between the emitter of said error currentdetecting transistor and said junction between said constant currentdetecting resistor and said exciter lamp, and said switch is connectedbetween said collector resistor of said error current detectingtransistor and the collector of said error current detecting transistor.3. Electric current according to claim 1, wherein a constant voltagediode is connected between the emitter of said error current detectingtransistor and said junction between said constant current detectingresistor and said exciter lamp, and said switch is connected between thecollector of said error current detecting transistor and said otherterminal of said electric source.
 4. Electric circuit according to claim1, wherein the base of said current control output transistor isconnected through the collector-base path of a further transistor to thecollector of said error current detecting transistor, said collector ofsaid further transistor being connected to said one terminal of saidelectric source through a collector resistor thereof while the emitterthereof is connected to the emitter of said error current detectingtransistor, and the base of said error current detecting transistor isconnected through a first voltage dividing resistor to said junctionbetween said current control output transistor and said constant currentdetecting resistor while said base is connected to said junction betweensaid constant current detecting resistor and said exciter lamp through asecond voltage dividing resistor, said switch being connected betweenthe collector of said error current detecting transistor and saidcollector resistor of said error current detecting transistor. 5.Electric circuit according to claim 1, wherein the base of said currentcontrol output transistor is connected through the collector and thebase of a further transistor to the collector of said error currentdetecting transistor, said collector of said further transistor beingconnected through a further collector resistor to said one terminal ofsaid electric source while the emitter thereof is connected to theemitter of said error current detecting transistor, and the base of saiderroR current detecting transistor is connected through a first voltagedividing resistor to said junction between said current control outputtransistor and said constant current detecting resistor while said baseis connected to said junction between said constant current detectingresistor and said exciter lamp through a second voltage dividingresistor, said switch being connected between said other terminal ofsaid electric source and the collector of said error current detectingtransistor.